Memristor switch devices, which are often formed of nanoscale metal/titanium oxide/metal layers, typically employ an “electroforming” process to enable resistive switching. The “electroforming” process involves a one-time application of a relatively high voltage or current that produces a significant permanent change of electric conductivity through the titanium oxide layer. The electrical switching arises from the coupled motion of electrons and ions within the oxide material. During the electroforming process, oxygen vacancies are created and drift towards the cathode, forming localized conducting channels of sub-oxides in the oxide.
The localized conducting channels are formed to include a small gap between the ends of the conducting channels and a metal layer. The gap typically forms about a 2 nm-wide tunnel barrier at the tops of the conducting channels. As voltage is applied, oxygen vacancies are driven out of the conduction channel into the barrier region, which changes the resistance of the memristor switch device. The diffusion constant for the oxygen vacancies is practically zero at room temperature. As such, in the absence of an applied bias voltage, the oxygen vacancies will remain in the barrier region and the memristor switch device will retain its state at room temperature.